1. Field of the Invention
The present invention relates to a method for adjustment and/or indication of a liquid or gaseous pressure, and a device for utilization of the method.
2. Description of the Prior Art
In installations including parts such as pipe systems or similar apparatus for liquid or gas under pressure, it is previously known to use different types of valve members for pressure adjustment, such as safety valves, overflow valves and similar devices, and also to use different types of indicating members, e.g. pressure gauges, intended to show existing pressures.
With regard to previously known types of valve members, these usually include a piston member, having a surface communicating with the medium under surveillance, said piston member usually being arranged in contact with a valve seat or similar element due to pressure from a co-acting spring member. With regard to safety valves, arranged in a water pipe system, e.g. in connection to incoming pipes for a hot water boiler, the valve member is designed and arranged in such a way, that it will open at a pipe pressure exceeding a predetermined limiting value, thus eliminating damage caused by intermittent and large pressure increases in incoming pipe system. Said type of valve usually includes a circular valve member having a relatively large diameter, arranged in contact with a valve seat under the influence of a spring, said valve seat communicating with the incoming pipe system. When the pressure is increased above a predetermined value, said valve member is forced in a direction away from the valve seat, whereby the water can flow out from a discharge channel in a surrounding valve housing. In order to faciliate control of the valve, a manually operable member is arranged outside the valve housing, which by application of a considerable manual force is arranged to move the valve member in a direction away from the contact position against the valve seat. This makes it possible to check that the valve member can perform the intended opening movement.
Previously known types of overflow valves normally include a piston or a ball, which is spring loaded in contact with a valve seat. The tension of the spring is normally adjustable, e.g. by means of an adjustment screw, whereby desired opening pressure can be preadjusted. When the piston, or the ball, is moved from the contact position with the valve seat when preset pressure is exceeded, the medium comunicating with the valve seat is transferred to a suitable point in the system by means of an overflow channel.
With regard to previously known types of pressure indicating members, these usually include a spring loaded piston, the movement of which is a measure of existing pressure, or a bent tubular part, closed at a free end portion, and with the other end portion communicating with the medium under pressure to be indicated. The bent tubular part is usually attached to an indicating member by means of a lever system or similar mechanism, and the inclination to take up a linear configuration when exposed to an internal pressure is a movement which can be transformed to a measured value for existing pressure.
A common feature for previously known types of adjusting or indicating members used for liquid and gas under pressure is the use of spring loaded members, or members having spring-acting properties, in order to determine pressure limits and/or existing pressure. It is a known fact, that pressure springs, tension springs and helicoil springs extending in mainly one plane, as well as other types of springs, due to the properties of the material can not achieve the theoretically desired property, and that spring movement does not result in an altered spring load. With regard to pressure springs, the spring load is increased when the spring is compressed, if the spring has similar cross-sectional area along its entire length. By continuosly changing the relationship between cross-section/length, a certain compensation can be achieved, but the spring will be extremely costly to manufacture and calculate. Due to imposed stresses, caused by changes in temperatures and spring movements, the original properties of the spring are also altered. With regard to all types of springs, there is also an obvious risk of breakage, caused by variations in temperature and thereby changes in material properties, as well as other imposed stresses. With regard to pressure indicating members, such as pressure gauges, it is also difficult to achieve a member which faciliates a linear display of existing gaseous or liquid pressure, e.g. by the movement of a pointer along a scale. The sensitivity for temperature changes is also high for this type of instrument, i.e. changes in temperature near the instrument influence the spring members, which causes faulty indications. Calibration is also often necessary with certain intervals of time, in order to compensate for indication faults caused by changes in spring acting members, due to previously mentioned imposed stresses and ageing phenomena.